Originally Posted by
KerryIrons
The rule for chain replacement is 1/16" elongation, so your ruler is saying 50% and the chain checker is saying 75% (and might have read 25% on a brand new chain). And don't get confused that there is a magic "worn vs. not worn" point. Wear is linear, not digital. Things don't instantaneously get bad when chain wear crosses a threshold.
While Kontact is theoretically correct his example assumes a significantly different wear rate on rollers vs. pins, which is not the case. There are lots of examples of chain checkers being wrong, but rulers never lie.
My example shows how roller wear alone can damage the sprockets. But roller wear AND pin wear don't cancel each other out - together they are going to produce the geometrical effect depicted in the graphic - that the pitch of the chain is effectively different when curved around a sprocket.
What examples do you have of chain checkers being wrong? How did you test that they were wrong?
And the whole 25% thing is a canard. It doesn't matter what the chain measures until that measure exceeds whatever tolerance the manufacturer recommends as "No go". We don't measure the chain to monitor its wear - that wear might not be linear. We measure the chain to take note of whether it is still in-spec or not. When it is not, you replace it to keep the rest of the drivetrain in shape.